This invention relates to an ignition system for a small internal combustion engine, and more particularly to a breaker point arrangement for a magneto ignition system.
In an ignition system for a small internal combustion engine, for example a one-cylinder engine used to drive a small chain saw, the ignition pulses may be produced in response to the opening and closing of a pair of breaker points in timed relation with operation of the engine. One of the breaker points is stationary while the other breaker point is carried by a breaker lever which is resiliently urged against the stationary breaker point, and the breaker points are opened and closed upon movement of the breaker lever in association with the operation of the engine. The breaker points are typically arranged on a breaker plate as a unit for ease of assembly with the engine, and a capacitor is electrically connected across the breaker points to reduce electrical arcing.
In the past, the breaker points have often been mounted on a metal breaker plate having a turned-up ear supporting the stationary breaker point while the breaker lever is pivotally supported on a metal post which is staked to the breaker plate. The capacitor is typically contained in a metal can having an insulated lead for electrical connection with the movable breaker point, while the metal can serves as the other capacitor lead and is soldered to the metal plate for electrical connection with the stationary breaker point. The breaker point arrangement on the metal breaker plate is mounted as a unit in a cylindical opening formed in the engine casing, and the breaker plate is electrically grounded to the engine by a screw which secures the breaker plate to the engine casing.
However, with the advent of smaller less expensive chain saws requiring shorter periods of operation, it is desirable to provide a less expensive ignition system by reducing the cost of the breaker point arrangement. A substantial cost reduction could be achieved by utilizing a less expensive capacitor which is not contained in the metal can. However, the substitution of a less expensive capacitor is precluded by the operating environment of the breaker point arrangement which is subject to substantial temperature variations and mechanical vibrations. Moreover, the leads of such an inexpensive capacitor are uninsulated and could undesirably contact another electrical conductor.